1. Field of the Invention
The present invention relates to a person-detecting sensor employed in automatic water faucets, automatic flushers for urinals, and in like applications, and to automatic water faucets provided with such sensors.
2. Description of the Related Art
Automatic water faucets that automatically discharge water upon detecting a user's hand waving action, and automatic flushers for urinals that automatically supply flushing water upon detecting a user having drawn near have been known to date. Such automatic faucets and automatic flushers incorporate person-detecting sensors for detecting a nearby person. Known person-detecting sensors of this sort include a sensor in which a light-emitting element such as an LED and a light-receiving element such as a position sensitive detector (PSD) are arranged offset from each other.
This person-detecting sensor identifies the position where light reflected from a detection object is incident on the PSD and measures distance to the detection object by the principle known as triangulation. PSDs, exceedingly simple photodetectors that output a signal according to the position of the centroid of incident light, have the advantage of being low-power-consuming. On the other hand, with the information that can be acquired by a PSD being positional information only, the reality is that little can be done to deal with situations where external disturbance light has become incident. For that reason, erroneous detection may occur, for example, in an automatic water faucet on a sink where a person-detecting sensor including a PSD is employed, due to the influence of external disturbance light such as light specularly reflected from the washing bowl.
A person-detecting sensor proposed in order to improve detection performance uses an imaging element such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) (reference is made, for example, to Patent Document 1). With person-detecting sensors employing an imaging element, the possibility exists that detection performance can be improved by, for example, eliminating the influence of external disturbance light by making use of information such as distribution of received-light quantity of each pixel. Sensors eliminating specularly-reflected light to reduce erroneous detection by exploiting the geometric characteristics of received-light waveforms that are waveforms of the distribution of the amount of light received by each pixel have been proposed as person-detecting sensors of this sort (reference is made, for example, to Patent Document 2).
Patent Document 1 Japanese Pat. App. Pub. No. 2005-207012
Patent Document 2 Japanese Pat. App. Pub. No. 2012-77472
Nevertheless, problems such as the following still remain with person-detecting sensors in which attention has been focused on the shape of received-light waveforms to eliminate specularly-reflected light. Namely, when a number of beams of specularly-reflected light are incident while being superimposed on one another, the shape of the received-light waveform can differ from that of the original specularly-reflected light and become similar to diffusely-reflected light from the surface of a person, meaning that eliminating the beams as specularly-reflected light may prove impossible, and running the risk that erroneous detection will arise. In particular, situations where a person-detecting sensor in which a detection region that is set toward a concave bowl surface such as a washing bowl can lead to beams of specularly-reflected light arising simultaneously in a number of locations on the bowl surface, such that a number of beams of specularly-reflected light may become incident while being superimposed (synthesized) on one another.